The present invention relates to a rotating disk storage device such as a magnetic disk drive and a magneto-optic disk drive, and more particularly to a mechanism for giving supplementary force to a driving mechanism of an actuator.
A magnetic disk drive pivotally moves a head/slider, which is supported by an actuator assembly, approximately in a radial direction of a magnetic disk while floating the head/slider with a slight gap being kept on a recording surface of a rotating magnetic disk, and thereby reads and writes data. A load beam used to support the head/slider generates a pressing load in the form of a pressure in a direction in which the head/slider is pressed on the recording surface of the magnetic disk. This pressing load is balanced with the buoyancy which an air bearing surface of a slider receives from airflow occurring on a surface of the magnetic disk. As a result, a given gap is kept between the air bearing surface and the recording surface.
While the magnetic disk is rotating at the given number of revolutions, because the airflow occurring on the surface acts, there is little possibility that the recording surface of the magnetic disk will come into contact with the slider. However, if the head/slider is located above the recording surface of the magnetic disk, the rotation of which is stopped, the head/slider will land on the recording surface because the action of the airflow is also stopped. In this case, a lubricant applied to the recording surface, inter-attraction occurring between smooth surfaces, that is to say, between the recording surface and the air bearing surface, the pressing load of the load beam, and the like, cause the head/slider to be attracted onto the recording surface of the magnetic disk. If a spindle motor holding the magnetic disk is rotated with the head/slider being attracted, a phenomenon of sticktion occurs, which may make a flaw in the slider and on the surface of the magnetic disk or may hinder a motor from starting.
Accordingly, in a magnetic disk drive that adopts the load-unload method, when stopping the rotation of the magnetic disk, the head/slider is retracted into a retraction area provided by a retraction mechanism that is called a ramp mounted outside the recording surface of the magnetic disk. In the event that the power supply is suddenly interrupted while the head/slider accesses the recording surface of the magnetic disk, no energy is available to drive an actuator assembly into the retraction area. Therefore, a voice coil motor (hereinafter referred to as “VCM”) is driven by use of back electromotive force of the spindle motor coupled to the magnetic disk rotating by momentum, and an electric charge stored in a capacitor of an electronic circuit, to move the actuator assembly to a retraction position before the rotation of the magnetic disk stops. This is one way to prevent the sticktion from occurring.
With the progress of the miniaturization of magnetic disk drives, the number of turns of a voice coil, and a thickness of a voice coil magnet influencing on magnetic field strength of a yoke gap, are limited by spatial limitations. Therefore, it has become increasingly difficult to obtain a high torque from a VCM. Moreover, there are many limitations in the amount of back electromotive force of a spindle motor and the amount of an electric charge to be accumulated in a capacitor. Accordingly, in the case of the small-size magnetic disk drive, it is more difficult to reserve the energy for securely retracting a head/slider into a ramp in the event of interruption of the power supply, and also to obtain the torque required for pivotally moving an actuator assembly, as compared with a large-sized magnetic disk drive. This increases the possibility that sticktion will be caused by a failure in retraction.
Moreover, when a slight shock or vibrations are applied to the magnetic disk drive from outside after the actuator assembly has retracted to a home position of the ramp, if there is no mechanism for holding the actuator assembly at the home position, there is a possibility that the actuator assembly will gradually move toward the recording surface side of the magnetic disk and eventually the head/slider will jump on the recording surface. As a mechanism for holding the actuator assembly at the home position, there is a method in which a magnet is embedded in a crash stop. However, the strength of the magnet is limited to a range within which the actuator assembly can leave by the torque of a voice coil motor.
Therefore, even if the magnet is embedded in the crash stop, there may be a case where the actuator assembly cannot be held reliably at the home position. In addition, a size of the crash stop is also enlarged, which is not desirable for the miniaturization of the magnetic disk drives. Heretofore, there was a technology for producing attraction between a voice coil magnet and a metal chip embedded in a coil support to hold the actuator assembly at its home position. However, there is a limit in attraction as described above. As a result, the actuator assembly sometimes moved from the home position. What is more, the attraction could not also be utilized as retraction energy at the time of power shutdown.